Modeling Target Defects in Direct-Drive Inertial Confinement Fusion

A range of experimental and simulation evidence suggests that isolated defects on the outside of cryogenic targets are able to play a significant role in degrading direct-drive inertial confinement fusion implosion performance, particularly in implosions with a low in-flight adiabat. A cryogenic target may have dozens of these defects, which originate during the high-pressure permeation fill and cooling cycle, and range in size from microns to tens of microns. Both simulations and experimental data have shown that small-scale laser imprint, while capable of generating hydrodynamic mix, does not appear to be the dominant mechanism of mixing ablator material into the hot spot. Previous modeling of defects tens of microns in size has shown that the resulting local perturbation growth can inject ablator mass into the hot spot, contributing to radiative cooling and loss of performance. In this talk we present the results of multidimensional simulations of smaller (micron-scale) defects in the context of more recent cryogenic target designs, addressing both the reduction in areal density and the transport of ablator material into the hot spot.